Improving the long-term stability of bismuth alloy well plug systems

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Hydrocarbon resource development is a key driver of the Canadian economy. This has led to the emission of harmful gases, the build-up of carbon dioxide (CO2) in the atmosphere, and the potential for contaminating ground water from wells. Whether lowering pollution, employing hydraulic fracturing, or sequestering CO2 underground, strategic plugging of old and redundant wellbores is critical. Of the roughly 400,000 wells in Alberta in 2012, the number of wells that need to be properly plugged could well exceed 50,000, and this number is growing dramatically. Although Alberta leads the world in tough standards governing the unintended contamination of ground water and release of particularly harmful gases, plugging technologies have not kept pace with the vast number of wells that need to be retired. Seal Well Inc., an Alberta-based company, has patented an alternative wellbore plugging technology based on a bismuth-tin (Bi-Sn) alloy that should be less costly to install, while being far more reliable than current methods. To adapt this technology to the growing use of highly corrosive, pressurized CO2 for enhanced oil recovery and CO2 sequestration, it is necessary to demonstrate that the Bi-Sn alloy and the surrounding steel will have the useful service life needed to form a permanent plug. The focus of this project is to determine the corrosion susceptibility of the Bi-Sn alloy /steel system under realistic down-hole conditions and address corrosion issues encountered from acid gas attack through a combination of strategies. For the first time, a method of applying corrosion inhibitors and oxygen scavenger to Bi-Sn/steel systems will be developed and tested in CO2-saturated brine. Also, the surface structure of the Bi-Sn alloy will be modified to make it more corrosion resistant, and methods of electrolytic cathodic protection and addition of protective Bi coatings onto the Bi-Sn surface, will be explored. The outcome of this work will be the significant extension of the useful service life of the Seal Well technology under harsh underground conditions, thus containing a significantly escalating pollution problem throughout the world, as well as the training of a large number of personnel in corrosion technologies.